Three sites in the southern Italian Apennines were selected to assess correlation between forest structure and bryophyte flora. In two of the sites, the Index of Air Purity (IAP)–based on cover data of epiphytic bryophytes–was evaluated. The results show that bryophyte populations–and consequently IAP–are affected by forest structure and development, and that studies including different sites require a precise assessment of silvicultural characteristics to allow comparisons. Indicator values of mosses and liverworts were also taken into consideration in characterizing ecologically the three sites.

Bryophyte Flora, forest structure, IAP, indicator values, silviculture

Bryophytes are a popular tool for the assessment of air quality in polluted urban areas, showing, together with lichens, all the necessary characteristics for a good bioindicator. They are sensible to polluting agents, stay in place in the area of study, have wide distribution and a life cycle sufficiently long, and they can accumulate pollutants in their body (Aleffi 1998; Govindapyari et al. 2010). De Sloover proposed in 1964 an Index of Atmospheric Purity (IAP) to assess air pollution and based on cover data of epiphytic lichens (De Sloover 1964; De Sloover and LeBlanc 1968) and epiphytic bryophytes (LeBlanc and De Sloover 1970). The IAP is extensively applied in cities and urban areas (e.g., Aleffi 1992; Dymytrova 2009; Zechmeister and Hohenwallner 2006) to supplement static and mobile monitors (for CO, CO₂, SO₂, O₃, NO_x), or satellite monitoring systems to assess particulate matter pollution, ground-level ozone, carbon monoxide and other major contaminants in wider areas. The limit of these monitoring devices is that they do not give information about the effects of air contaminants at the ecological level. The aim of this study is to verify the use of the IAP method (selected because of its widespread use and the possibility to have comparable results) in the assessment of environmental pollution in managed forested environments. Cryptogamic communities are conditioned by the developmental stage of the forest (Barkman 1958), and bryophytes, in particular, are important ecological components of managed forests. Bryophyte flora and vegetation provide information on the conditions of a forested area, its structure, ecology and climate at a given time (Brunialti et al. 2010). To further characterize ecologically the areas under study, and to evaluate the effectiveness of the Indicator Values of Mosses and Liverworts (Düll 1991), non-epiphytic bryophyte species have been considered. These indicator values were originally developed for Central Europe, but they appear to be usable also in internal mountain areas of southern Italy. The numerical values of these ecological indicators (varying from 1 to 9) are: Light number (L), from deep shade plants to full light plants. Temperature number (T), from cold to extreme warm indicators (from alpine to lowland, or from the Arctic to the Mediterranean zone). Continentality number (C), from euoceanic to eucontinental (from the Atlantic coast to the interior of Eurasia). Moisture number (M), from great dryness to permanently wet or sprayed, near waters or waterfalls, in water). Reaction number (R), from strong acid to base and lime indicators. The Median value is then calculated. Chorological values were also considered, but are not presented here.

The study sites were analyzed by determining their flora (bryological and vascular), climate, geology, pedology. Plots were established and silvicultural parameters calculated (tree-structure and developmental stage).

The IAP (sites A and B) was calculated according to the method presented by LeBlanc and De Sloover (1970) as partially modified by Nimis (1990). In particular, (1) a 60 x 50 cm grid–divided into 20 units of 10 x 15 cm–was placed on the trunk of each tree at a height (lower side) of 80–100 cm, in areas with the highest bryophyte density; (2) The IAP was calculated based on the following formula:

$\mathrm{IAP}=\sum _{i=1}^n(\mathrm{Q}\mathrm{i}\times f\mathrm{i}/10)$ ,

where 𝑓_i is an index of frequency/cover varying from 1 to 5; Q_i is the number of species accompanying any other species in each relevée (a factor of resistance to pollution).

The division by 10 is arbitrary and was indicated in the original formula by LeBlanc and De Sloover (1970) to obtain smaller numbers. These values are based on the diversity of epiphytic bryophyte populations, on the resistance to pollution of each species, on the phorophytes, and, in our case, on the forest structure and stage of development. Values of IAP recorded in the literature in urban areas vary according to the distance from the pollution source and the ecological conditions of the site (Nimis 1999). Values may vary from close to zero (indicating air pollution) up to values of 50 or more (indicating lack of air pollution).

The bryophyte vegetation was considered in three sites: (Site A) a managed forested area with Quercus cerris L. (Turkey oak) prevalent, and Quercus pubescens Willd. (Downey oak) sporadic, near an Oil hub; (Site B) a forested area with Fagus sylvatica L. (Beech). The IAP was determined in both sites; (Site C) a mountain area with a Fagus sylvatica-Abies alba Mill. (Beech-Silver fir) coenosis. The Indicator Values of mosses and liverworts were calculated for all three sites.

The main silvicultural and bryological (Indicator Values) results are presented for each of the areas considered. (Plots have a diameter of 20 m, and are located at a distance of 60 m one from the other.)

P=Plot; TBA=Total Basal Area (m²); ABA=Average Basal Area (m²); AD Average Diameter (cm, min.-max). IAP=Index of Air Purity (Sites A and B only).

Site A – The silvicultural data show there has been, as expected, an increase in the average diameters in the three plots after 5 years, which is reflected also in the values of total and average basal areas. This increase in diameter has affected the number of epiphytic bryophyte species recorded. Downey oak was not considered in the measurements, being a much better phorophyte. Plot 4 of 2008 was made up of very young plants with smaller diameters, too small to have any significant epiphytic vegetation. IAP could not be calculated (NC). Overall, TBA values appear low, indicating a forest in the first stages of development. The Indicator values of mosses and liverworts–reflecting the general ecological conditions of the site–have not changed from 2003 to 2008, as expected.

Site B – Plot 1 was cut more recently than Plot 2, as indicated, altering the number of epiphytes capable to attach and grow on the bark, and resulting in different IAP values. These values, in both plots, are quite low, not much different from those obtained in Site A which was exposed to pollution. This may be due to the type of forest management applied, with younger trees prevailing, and lacking the time to reach an equilibrium (as shown by low TBA values). The Indicator values appear to be almost identical in the two plots. Plot 1 has the same values, while Plot 2 diverges only for M = 3 (dryness); this is due to its position near the tree line and the uppermost montane grassland (edge effect) exposing to the sun the bryophytes from the inside, as it was shown by Hylander (2005).

Site C – This forest is characterized by silver firs. Beeches become more frequent in the higher parts of the submontane belt, as compared to other broadleaf trees (Plot 1). In this belt, the presence of all diametrical classes of silver firs in reproductive age has been recorded (an abundant production of cones was observed during Fall 2002). Silver firs here are taller than beeches, and their canopy is directly exposed to sun rays. Their spatial distribution varies from isolated plants within a stand of beeches, to pure populations with an extension of even a few thousand square meters exhibiting the micro-environmental conditions of pure silver fir forests. At higher altitudes (Plot 2) beeches become the dominant trees and silver firs almost disappear (even though old big stumps and rotting logs are still visible). Silver firs are still relatively abundant in the sub-canopy layers as individuals of about 1–4 m of height in a “waiting” phase, many with the vegetative apex damaged by grazing or by contact with branches of higher trees. The Indicator values show that bryophytes of xeric or Mediterranean environments prevail at lower elevations, while at higher elevations, at the tree line, species with a sub-Oceanic (and sub-Mediterranean) ecology prevail, as expected given the different ecological conditions previously indicated.

The values of IAP obtained in this study need consideration, and an explanation. These values are lower in Site A, near a source of pollution, and higher in site B, with no apparent pollution source, as expected. The IAP values in site B, however, are much lower than those normally obtained in unpolluted urban areas. This may be related to the silvicultural management systems applied, with frequent cutting of trees and resulting low TBAs, altering adversely bryophyte diversity because of their vulnerability to microclimatic changes (Perhans et al. 2009). Further study is required to compare IAP values from forest sites to those obtained in urban areas; the determination of correction factors (possibly based on TBA values, and phorophyte selection) is necessary. A preliminary strategy–limited to forested areas, would be to consider stands at the same stage of development and with comparable management systems, better if aged (Hébrard 1989). The effectiveness of the Indicator values for mosses and liverworts for the areas considered was verified both spatially (sites A, B, and C) and temporally (site A).

I thank colleagues and students who assisted me in the field in some of the studies reported here. Among them, I thank in particular, Enza Evangelista, Carmine D’Avella, and Filippo Verova.